This invention relates to a method for installing a flange on the end of a tubular member lined with a thermoplastic liner, a novel flange construction and the lined flanged tubular member.
The lining of tubular members with plastic pipeliners achieves several desirable results. Firstly, such liners are used to repair pipelines which have developed cracks or leaks through which conveyed fluid may be lost. Such liners are also used to protect metal pipelines from internal corrosion resulting from the corrosive nature of the conveyed fluid. In the case of oil field pipe, many of the fluids transported for completion, stimulation or production have a detrimental effect on the metal from which the pipe is constructed.
In addition to use in oil field applications, lined tubular members also find wide application in the irrigation field. In this case, it is desirable to protect the metal pipelines from internal corrosion, and at the same time provide suitable joints so that long sections of tubular members can be flanged together to provide water at far distances from the source.
The plastic pipeliners which are installed within metal tubular members are usually thermoplastic materials. These materials can be heated to a temperature and for a time sufficient to render the material to a malleable state so that the material can be formed into a desired shape. The term "plastic" is intended to include, for example, polyethylene, polyvinyl chloride, polyvinyl chloride-acetate, polystyrene and the like.
In the case of flanged metal pipelines, various adapters have been provided in the past for joining sections of pipelines as well as the associated sections of plastic liners. In one such prior art technique, the adapters were fused onto the plastic liner ends which protrude from the section of metallic pipeline. Since the adapters were of a fixed length, it was necessary to calculate accurately the expansion/contraction characteristics of the plastic liner material installed within the section of metal pipeline to prevent the adapters from being pulled out of position upon contraction of the liner. In other prior art techniques, an exposed portion of the plastic liner was bent backwards at an angle or "flare" to form-a-flange on a plastic liner. U.S. Pat. No. 3,142,868 to Blout, issued Aug. 4, 1964 is typical of this type of prior art approach. Here, a mechanical device is utilized to flare a liner extending from a tubular member. The process also involves heating, supporting and cooling the flared end.
The inventors have also developed reinforced flanges on plastic pipeliners suitable for use in high pressure applications. A reinforced flange is disclosed in U.S. Pat. No. 5,094,795 issued on Mar. 10, 1992 and U.S. Pat. No. 5,171,041 issued on Dec. 15, 1992 to McMillan and Tarsha. In this prior art device, a reinforced ring having a rigid portion and an elastomeric portion is placed about the liner exterior and a retaining ring is placed about the reinforced disk. A forming unit is used to apply heat to the liner and force it to flip into a reformed shape having a greater external diameter than the remainder of the liner. While this method is entirely satisfactory, it is desirable to provide a more economical approach for use in irrigation systems.
The inventors herein have also disclosed a method for forming a flange on the end of a plastic pipeliner utilizing a preformed synthetic disk installed on the end of the liner which extends from the tubular member. The exposed end is surrounded with a heating unit which heats the junction between the preformed disk and exposed end of the liner to form a weld area between the two elements. This method is also entirely satisfactory, but requires a wide variety of preformed disk having a variety of accurately formed central bores for placement on the extended portion of the liner. This method of forming a flange is disclosed in U.S. Pat. No. 5,462,706 for "Method for Forming a Flange on an End of a Synthetic Liner" which issued on Oct. 31, 1995, to McMillan and Tarsha.
The early prior art techniques such as Blout suffers from the shortcoming that the liner flange end could be drawn longitudinally inwardly into the interior of the tubular member upon contraction of the liner material. Other prior art liners are designed to overcome this shortcoming, but it nevertheless remains desirable to provide an improved method for forming a liner when a blow out protection ring is not needed and it is desirable not to have to couple two separate elements to form a flange.